1. Field of the Invention
The present invention relates to a CDMA (Code Division Multiple Access) communication system, and more particularly to an orthogonal code hopping multiple access (OCHMA) communication system which divides channels according to the hopping patterns of the orthogonal codes.
2. Description of the Related Art
FIGS. 1A and 1B are block diagrams illustrating the construction of a conventional CDMA communication system using orthogonal codes, wherein FIG. 1A shows a transmitter and FIG. 1B shows a receiver. Here, the orthogonal code may be a Walsh code, a Hadamard code or a Gold code.
Referring to FIG. 1A, an orthogonal code generator (OCG) 10 generates orthogonal codes OC(o)-OC(m) for the respective digital signals Do-Dm output from signal sources 9a-9c. Mixers 11a-11c mix the digital signals Do-Dm with the corresponding orthogonal codes OC(o)-OC(m), and a summer 12 sums the mixed signals output from the mixers 11a-11c. A pseudo-noise sequence generator (PNSG) 13 generates a pseudo-noise sequence (PNS) or a pseudo-random sequence (PRS). A mixer (or multiplier) 14 multiplies an output signal of the summer 12 by the PNS, and a modulator 15 modulates an output signal of the mixer 14 into a RF (Radio Frequency) signal. A power amplifier 16 amplifies the RF signal and transmits the amplified RF signal through an antenna 17.
Referring to FIG. 1B, an RF amplifier 21 amplifies the RF signal received via antenna 20. Demodulator 22 demodulates the RF signal output from the RF amplifier 21 in sync with a sync signal transmitted from the transmitter of FIG. 1A. A mixer (or multiplier) 24 multiplies the demodulated signal output from the demodulator 22 by the PNS generated from an PNSG 23. An orthogonal code generator 28 generates orthogonal codes OC(o)-OC(m) identical to those in the transmitter. Mixers (or multipliers) 25a-25c multiply the output signal of the mixer 24 by the corresponding orthogonal codes OC(o)-OC(m). Integrators 26a-26c integrate the output signals of the mixers 25a-25c to restore the original digital signals Do-Dm and transfer the restored digital signals to the respective signal destinations 27a-27c. 
As appreciated from the foregoing, in order to divide the channels, the conventional CDMA communication system allocates the unique orthogonal codes belonging to a specified set of the orthogonal codes to the respective channels and repeatedly multiplies the transmission digital signals by the allocated orthogonal codes. That is, the transmitter of FIG. 1A repeatedly multiplies the allotted orthogonal codes for the bit duration of the digital signal to be transmitted, to spread the digital signal so that the spread digital signal may have wider spectrum than the original digital signal. In addition, the transmitter multiplies the transmission signals by the PNS to scramble the transmission signals so that the other terminals may not restore the scrambled transmission signals. The receiver of FIG. 1B executes a reverse process of the transmitter. That is, the receiver generates the PNS identical to that used in the transmitter and multiplies the received RF signal by the PNS. The receiver then further multiplies the RF signal by the orthogonal codes identical to those used in the transmitter, repeatedly, and integrates the signals for the bit duration of the digital transmission signal, thereby restoring the original digital signals.
As is apparent from the foregoing description, when the digital signals have not been previously encrypted, the conventional CDMA communication system multiplies the digital signals by an agreed PNS between the transmitter and the receiver so as to encrypt the digital signals.
Accordingly, it is an object of the present invention to provide an orthogonal code hopping multiple access communication system which divides channels in accordance with hopping patterns of orthogonal codes allotted to the respective channels.
To achieve the above object, the CDMA communication system comprises a transmitter for modulating input digital signals using an orthogonal code hopping multiple access technique and transmitting the modulated digital signals, and a receiver for receiving the digital signals using the orthogonal code hopping multiple access technique and restoring the digital signals.
According to an embodiment, the transmitter comprises a first hopping orthogonal code generator for generating orthogonal codes according to a hopping pattern prescribed between the transmitter and the receiver; a plurality of mixers each connected to the first hopping orthogonal code generator, for multiplying the digital signals by the corresponding orthogonal codes; a summer connected to outputs of the mixers, for summing the output signals of the mixers; a modulator for modulating an output signal of the summer; an antenna; and a power amplifier for amplifying an output signal of the modulator and transmitting the amplified signal through the antenna.
The receiver comprises an antenna; a radio frequency (RF) amplifier for amplifying an RF signal received through the antenna; a demodulator for demodulating an output signal of the RF amplifier; a second hopping orthogonal code generator for generating orthogonal codes according to a hopping pattern identical to the hopping pattern in the transmitter; a plurality of mixers for multiplying an output signal of the demodulator by the corresponding orthogonal codes; and a plurality of integrators for integrating output signals of the mixers to restore the digital signals.
The first and second hopping orthogonal code generators each comprising an orthogonal code generator for generating the orthogonal codes according to the hopping pattern; and a hopping controller connected to the orthogonal code generator, for generating the hopping pattern and providing it to the orthogonal code generator.
In an alternative embodiment, each the first and second hopping orthogonal code generators comprise a memory for storing the orthogonal codes, and for outputting the orthogonal codes according to the hopping pattern; and a hopping controller connected to the memory, for generating the hopping pattern and providing it to the memory.